As is well known, the compressor case of a gas turbine engine powering aircraft is subjected to severe pressure and temperature loadings throughout the engine operating envelope and care must be taken to assure that the components remain concentric maintaining relatively close running clearances so as to avoid inadvertent rubs. Inasmuch as the engine case is thin relative to the rotor and stator components in the compressor section, it responds more rapidly to temperature changes than do other components. This is particularly true during periods of transient engine performance. Typical of these transients are throttle chops, throttle bursts, and the like. Obviously it is customary to provide sufficient clearances during these transients to assure that the rotating parts do not interfere with the stationary parts.
The problem becomes even more aggravated when the engine case is fabricated in two halves (split case) which is necessitated for certain maintenance and construction reasons. Typically, the halves are joined at flanges by a series of bolts and the flanges compared to the remaining portion of the circumference of the case are relatively thick and hence do not respond to thermal and pressure changes as quickly as the thinner portion of the case. The consequence of this type of construction is that the case has a tendency to grow eccentrically or out of round.
In order to achieve the roundness and clearance control of the stationary an rotating components it was necessary to incorporate a mechanism that would tie the outer case to the segmented stator components. It also is important to assure that rubbing does not occur, particularly where severe rubbing could permanently damage the blades and/or rotor/stator during surge. The mechanism that is utilized must be capable of withstanding enormous load, yet be insensitive to fatigue. Flexibility is required in the configuration while maintaining fixed hardware. The problem is more aggravated since the engine is designed to avoid surge and surge may be non-existing so the part used to solve the problem only has utility during a circumstance that may not occur. Thus, it is abundantly important that it doesn't present a maintenance problem, i.e. require early removal because of fatigue. Furthermore, it shouldn't be unduly heavy, since weight would impact overall engine performance.
We have found that we can obviate the problems noted above, or at least alleviate the same, by providing a relatively thin arcuate shaped rail trapped in hooks extending from the segmented stator ring that supports the stator vanes in the compressor for tying the outer axially split case. This permits the use of the split case and concomitantly facilitated the assembly of the compressor section.